Hydromechanical method and device for the reverse redrawing of sheet metal

ABSTRACT

Blanks for sheet metal are drawn with the aid of a pressure container, a liquid displacing annular plunger pressure tightly glidable in the container and having a top adapted for accommodating the blank, a holddown for pressing the blank against the top, and a draw punch passing through the holddown. The container and plunger are first filled with liquid up to the top. Then the blank is placed onto the top, whereafter the holddown is forced downwardly against the blank, thereby pressing the plunger into the container. The increasing liquid pressure in the container draws the blank to a shape bulging upwardly into the holddown. Thereafter, the blank is reversely redrawn into the pressure container by pressing the punch from above against the blank and downwardly into the container.

United States Patent [72] inventor Eugen Burk Traunstein, Germany [2]]Appl: No. 857,030

[22] Filed Sept. 11,1969

[45] Patented Aug. 3, 197i Siemens-Electrogerate G.m.b.H. Berlin &Munich, Germany [32] Priority Sept. 12, 1968 [33] Germany [73] Assignee[54] HYDROMECHANICAL METHOD AND DEVICE FOR THE REVERSE REDRAWING OFSHEET METAL 7 Claims, 4 Drawing Figs.

[52] U.S.Cl 72/57, 29/42] [51] Int. Cl B211! 26/04 [50] Field Of Search7267,60;

[56] References Cited UNITED STATES PATENTS 3,208,255 9/l'965 Burk 72/573,504,070 3/1970 Zaharskl 18/19 Primary Examiner-Richard J. HerbstAlrorne vsCurt M. Avery, Arthur E. Wilfond, Herbert L.

Lerner and Daniel J Tick ABSTRACT: Blanks for sheet metal are drawn withthe aid of a pressure container, a liquid displacing annular plungerpres sure tightly glidable in the container and having a top adapted foraccommodating the blank, a holddown for pressing the blank against thetop, and a draw punch passing through the holddown. The container andplunger are first filled with liquid up to the top. Then the blank isplaced onto the top, whereafter the holddown is forced downwardlyagainst the blank, thereby pressing the plunger into the container. Theincreasing liquid pressure in the container draws the blank to a shapebulging upwardly into the holddown. Thereafter, the blank is reverselyredrawn into the pressure container by pressing the punch from aboveagainst the blank and downwardly into the container.

, msqnmjnmcn ME'rnonANu Device iron T e a container and adapted forreceiving the sheet-metal blank, a

holddown which presses the blank against the plunger top, and a drawingpunchwhich passes through the holddown.

It is known to shape a blank of sheet metal hydromechanically by firstpredrawing a blank with the aid of the conventional drawing method,using an ordinary dieandpunch blank 7 been placed upon the top of theplunger i. When the tool assembly closes; the holddown '8 moves'againstthe blank 14 and presses it onto the seal ii, the downward travel of theholddown relative to the plunger 4 being limited by spacers l4.Thereafter, the downwardly travelling plunger Al is forced into the toolbottom portion ll. The spacers 114 are so dimensioned'that, whilepermitting a slight deformation of the blank 7, they receive thepressing force from the holddown 8 and transmit it to the displacingplunger 4. The displacing plunger 4 thus is pressed into contact of itstop flange with the tool bottom portion 1 (FIG. 2), while thecorrespondingly in-, creasing liquid pressure draws the blank 7 to thecup shape ap' parent from FIG. 2. The bottom of the draw punch 9 maythen form a limiting stop. However, additional stops or abutments mayalso be inserted so as to form part of the holddown member.

press. Thereafter, the. preshaped workpiece is reversely,

redrawn by the hydrornechanical method. The two assemblies known forsuch purposes have the disadvantage that due to the necessity of firstapplying a conventional drawing operation,the equipment is rathercomplicated and expensive whilestill falling short of providing foroptimal drawing conditions during the predrawing operation.

, It is an object of my invention to provide a reverse redrawing methodvand device with whose aid'a double-acting drawing press affordspredrawing and reversely redrawing the workpiece on the hydromechanicaldrawing principle.

To this end, and according to my invention, the pressure container andthe annular plunger glidable in the container are filled with liquid upto the top rim, whereafter the blank is placedupon theannular top of thedisplacement plunger and so loaded by the holddown'as to press thedisplacement plunger into the pressure container. The liquid pressurethus belng increased in the interior of the container and plunger isdeformed into the hollow space formed within the annular holddown and,as the case may be, also by the withdrawn drawing punch. This results inpreshaping the blank to a bulging or cup shape by the hydromechanicalaction. The blank,

thus preshaped, is then subjected to the downward drawing pressure ofthe punch which turns the bulging shape inside out and forces it intothe interior of the holddown or container.

The predrawing operation does not require any particular control orregulation of the liquid quantity because the volume er liquid displacedcan readily be so dimensioned as to render further control unnecessary.However, the reverse redrawing operation requires controlling the liquidto obtain a predetermined pressure because the volume of liquid in thepressure container must become reduced during redrawing.

Theinvention will be further explained with reference to an embodimentof a hydromechanical device according to the invention illustratedschematically on the accompanying draw ing, in which:

FIG. 1, 2 and 3 illustrate the reverse redrawing device in diametricalsection through the essential components and in three different drawingstages respectively; and FIG. 4 shows a modified detail of the samedevice.

The bottom portion 1 of the tool assembly, to be used in, or as part of,a punch press, is designed as a pressure container in whose interior 2an annular displacement plunger 4 is glidably displaceable. The plunger4 is provided with sealing rings at its periphery for maintaining aliquidtight and pressuretight seal.

. The top of the plunger 4 forms a flange above the container 1 and hasa top face 5 for accommodating a blank '7. A sealing ring 6 surroundingthe tubular hollow of the plunger t is in workpiece. This can be done,for example, by providing cor-- respondingly' adjustable or exchangeablestops between the bottom portion l and the displacing plunger 4, such asthe inserted stop 15 shown in FIG. 4.

FIG. 3 shows how thereafter the punch 9 reversely draws the predrawnworkpiece '7 into the pressure container. During this operation, liquidis issued from the pressure container into the tank 12 in accordancewith the predetermined pressure set by the control valve ill.

The liquid used for the method and device according to the invention maybe water.

It will be obvious that the device for performing the method accordingto the invention is not limited to the embodiment illustrated but that avariety of shapes can be drawn during the predrawing stroke as well asduring the reverse redrawing stroke. For predrawing it is merely to betaken into account redrawing operation.

s'erted for securing a liquidtight and pressur'etight seal during joperation of the device. The blank 7 is pressed against the seal 6 bymeansof an holddown member 8 whose hollow is traversed by a drawingplunger 9. The pressure space 2 within the tool bottorn portion 1 isconnected through pipes and a V check valve 10 as well as anoverpressure valve lll to a tank 12.

which receives compressed air through an inlet duct 13.

FIG. ,1 shows the tool assembly open. The interior of the pressure space2 within the tool bottom portion 1 and within the plunger 4 has beencompletely'filled with liquid and a invention.

I claim:

1. A hydromechanical reverse redrawing method for shaping blanks ofsheet metal with the aid of a pressure container, a liquid displacingannular plunger pressure tightly glidable in said container and havingoutside said container a top adapted for accommodating a blank, 21holddown for pressing the blank against the top and a draw punch passingthrough the holddown, which method comprises the steps of filling thecontainer and plunger with liquid up to the top, placing the blank ontothe top, forcing the holddown against the blank and thereby pressing theplunger into the containerwhereby the increasing liquid pressure drawsthe blank to a preshape bulging upwardly into the holddown, andthereafter reversely redrawing the blank into the pressure container bypressing the punch from above against the preshaped blank and downwardlyinto the container.

2. The method according to claim 1, which comprises maintaining thepressure in the pressure container during reverse redrawingsubstantially constant and simultaneously discharg ing from thecontainer a quantity of liquid corresponding to the reduction in liquidvolume displaced by the workpiece being reversely redrawn.

3. A hydromechanical reverse redrawing device for shaping blanks ofsheet metal, comprising an upwardly open container for pressure liquidhaving liquid supply ducts, a plunger having a hollow and being glidablyand pressure tightly displaceable in said container, said plunger havinga flange with a top outside and above said container and having scalablemeans on said top for receiving the workpiece blank across the hollow sothat the blank when pressed against the plunger forms a closure of saidcontainer, an holddown movable under pressure toward the container toforce the plunger into the container whereby the increasing liquidpressure draws the workpiece blank to a shape bulging upwardly into theholddown, and a draw punch vertically movable in the hollow of saidholddown for reversely redrawing the preshaped workpiece by pressing itfrom above into the container.

4. In a device according to claim 3, said punch, when in its topposition, forming within the hollow of said holddown an

1. A hydromechanical reverse redrawing method for shaping blanks ofsheet metal with the aid of a pressure container, a liquid displacingannular plunger pressure tightly glidable in said container and havingoutside said container a top adapted for accommodating a blank, aholddown for pressing the blank against the top and a draw punch passingthrough the holddown, which method comprises the steps of filling thecontainer and plunger with liquid up to the top, placing the blank ontothe top, forcing the holddown against the blank and thereby pressing theplunger into the container whereby the increasing liquid pressure drawsthe blank to a preshape bulging upwardly into the holddown, andthereafter reversely redrawing the blank into the pressure container bypressing the punch from above against the preshaped blank and downwardlyinto the container.
 2. The method according to claim 1, which comprisesmaintaining the pressure in the pressure container during reverseredrawing substantially constant and simultaneously discharging from thecontainer a quantity of liquid corresponding to the reduction in liquidvolume displaced by the workpiece being reversely redrawn.
 3. Ahydromechanical reverse redrawing device for shaping blanks of sheetmetal, comprising an upwardly open container for pressure liquid havingliquid supply ducts, a plunger having a hollow and being glidably andpressure tightly displaceable in said container, said plunger having aflange with a top outside and above said container and having sealablemeans on said top for receiving the workpiece blank across the hollow sothat the blank when pressed against the plunger forms a closure of saidcontainer, an holddown movable under pressure toward the container toforce the plunger into the container whereby the increasing liquidpressure draws the workpiece blank to a shape bulging upwardly into theholddown, and a draw punch vertically movable in the hollow of saidholddown for reversely redrawing the preshaped workpiece by pressing itfrom above into the container.
 4. In a device according to claim 3, saidpunch, when in its top position, forming within the hollow of saidholddown an abutment for limiting the upward draw of the blank.
 5. In adevice according to claim 3, said holddown having an inner width atleast 30 percent larger than that of said punch.
 6. A device accordingto claim 3, comprising stroke limiting stop means between said pressurecontainer and said displacing plunger.
 7. A device according to claim 3,comprising a liquid-collector tank and a pressure control valve throughwhich said pressure container communicates with said tank formaintaining in said container a valve-controlled pressure during reverseredrawing.